Multiple slides of sputa were being worked up for pneumonia. One set of slides was stained by Giemsa and read at SFGH where expertise with Giemsa was optimal due to regular use of this stain for PC over the past few years. Whenever possible, 2 extra slides from each patient were sent to NIH where one was stained by TBO and the other by a monoclonal antibody indirect florescent antibody stain. True positive sputa were those that were 1) positive by and 2 of the 3 methods, or 2) positive by TBO alone but with a very good morphologic cluster of PC or 3) positive by TBO alone but verified by a subsequent positive lavage within that same episode of pneumonia. Using these criteria, the results showed 59/60 or 98.3% sensitivity by IFA, 52/60 or 86.7% by Giemsa, and 43/47 or 91.5% by TBO. There were 29 true negative specimens and all 29 were negative by the three methods. Of 91 consecutive sputa submitted for evaluation, 60/91 or 66% were positive for PC, suggesting that sputum exam can be a useful diagnostic technique with very low invasiveness. IFA using monoclonal antibodies developed by J.K. detected 98.3%, with 1 false negative reaction. This compared to 86.7 by Giemsa and 91.5% by TBO. Specificity of all three methods was excellent, with no false positive occurrences.